In a known vehicle seat with a so-called active cushion ventilation (German Patent Document DE 39 03 303 A1), the seat and backrest cushions are equipped with what is known as a ventilation layer. Air is blown through the ventilation layer by a ventilation device and exits at the cushion surface. The air causes a cooling effect at the cushion surface and provides for the removal of transpiration moisture, i.e. perspiration. The ventilating air taken in by the ventilation device is air-conditioned by an air conditioner.
In order to avoid overcooling when the ventilation air is adjusted so as to be too cold, it has been suggested to take in the ventilation air from under the vehicle. When the vehicle is heated by sun radiation, this air is at approximately 35.degree. C. and, therefore, is clearly cooler than the cushion surface, which is heated to approximately 60-100.degree. C. (German Patent Document DE 196 28 698 C1). Since the normal skin temperature of a human being is approximately 35.degree. C., there is still a temperature gradient between the seat user and the ventilation air. As a result, this ventilation air can still carry away heat from the seat user to the environment in order to achieve climatic comfort. During what is known as "summer switching", the ventilation device is started automatically when the vehicle door is unlocked. As long as nobody has sat down in the seat, air at approximately 30.degree. C. blown through the ventilation layer of the cushions results in cooling of the significantly warmer cushion surface. When the vehicle seat is occupied, the ventilation air absorbs both heat and water vapor emitted by the seat user by transpiration. When the seat user perspires, an additional cooling effect is achieved due to evaporation. This is desirable as long as the seat user's skin temperature does not fall under the normal value of approximately 35.degree. C. However, if the cushion temperature falls below the skin temperature, then overcooling may occur. This impairs a feeling of comfort.
It is an object of the invention to improve a vehicle seat of the initially mentioned type such that, while a high climatic comfort is maintained in the seat and back area of the vehicle seat, the possibility of overcooling is eliminated.
In a vehicle seat having seat and backrest cushions, a ventilation device for ventilating the cushions and a heating device for heating the cushions are provided. The seat includes a control unit which, on an input side, is connected with a temperature sensor arranged in the backrest cushion and, on an output side, with an electric circuit of the ventilation device and the heating device. The control unit operates the ventilation and heating devices so that, at cushion surface temperatures which are measured by the temperature sensor and which are situated above an indicated value, it switches on the ventilation device or changes the ventilation device to a higher power stage, and/or switches off the heating device or changes the heating device to a lower heating capacity. At cushion surface temperatures which are below the indicated value, the control unit switches off the ventilation device or changes the ventilation device to a lower power stage, and/or switches on the heating device or changes the heating device to a higher power stage.
The vehicle seat according to the invention has the advantage of producing an optimal sitting climate with cushion temperatures in the range of the normal human skin temperature, which ensures dry clothing and skin, and also under extreme conditions which exist, for example, during long drives at high outside temperatures, when entering a vehicle heated by sun radiation, or when a perspiring or hot person enters a cold vehicle.
The temperature sensor is arranged in a lower area of the backrest cushion, and the lower area of the backrest cushion approximately covers loin areas of seat users of different sizes. The indicated value for the cushion surface temperature corresponds approximately to a seat user's skin temperature and, preferably, is about 34.degree. C.
The control unit may also be connected on the input side with a moisture meter arranged in the backrest cushion close to a cushion surface. Switching-on, switching-off and/or power changing of the ventilation device and/or the heating device takes place after a regulating function is performed by the control unit such that a cushion surface temperature is maintained approximately constant at a temperature which is in the range of the indicated value. Ventilation air maintains an approximately maximal absorption capacity for transpiration moisture. The ventilation device may take in air from below the vehicle seat.
According to a preferred embodiment of the invention, the control unit has a regulating function which is designed such that the powers of the ventilation and heating devices are appropriately adjusted such that, on the one hand, the cushion surface temperature remains approximately constant in the range of the indicated value and, on the other hand, an approximately maximal absorption of transpiration moisture by the ventilation air is maintained. This regulating function permits an optimizing of the seat temperature to be achieved, since the ventilation and the heating of the vehicle seat are coordinated with one another such that the cushion surface temperature corresponds approximately to the normal skin temperature of the sitting person. Moisture precipitated by transpiration is also carried away very fast. In this case, the cooling effect which occurs because of evaporation is also utilized without allowing the cushion surface temperature to fall below the skin temperature. The targeted heating of the ventilation air in a correspondingly adapted air quantity results in an increased carrying away of moisture, in dry clothing, and in a comfortable cushion temperature.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.